Carbon nanofiber (CNF) are graphene layers arranged as stacks of cones, cups or plates to create a cylindrical nanostructure. Carbon nanotubes (CNT) are graphene layers wrapped into perfect cylinders. CNF are easier to construct than CNT, making them up to 100 times cheaper and suitable for mass production. CNF also present numerous exposed edge places along their surface allowing better bond than their CNT counterparts. Most efforts have been concentrated on polymeric CNT/CNF composites due to dispersion problems. The results of adding carbon CNF to cement based materials has yielded mixed results. The successful addition of CNF to cement-based materials has many advantageous mechanical and electrical properties including increased strength, ductility, and conductivity.
Fiber research in concrete construction is an ongoing field. Short-fiber composites are a class of strain sensor based on the concept of short electrically conducting fiber pull-out that accompanies slight and reversible crack opening. For a fiber composite to have strain sensing ability, the fibers must be more conducting than the matrix in which they are embedded, have a diameter smaller than the crack length, and well dispersed. Their orientations can be random, and they do not have to touch one another. The electrical conductivity of the fibers enables the DC electrical resistivity of the composites to change in response to strain damage, moisture, or temperature, thereby making them suitable for sensing.
The structural behavior and self-sensing ability of concrete nanofibers aggregates (CNFA) allows for structural health monitoring for the reduction of maintenance and enhanced concrete construction. As a nonlimiting example CNFA can be used to monitor strain, water content, temperature changes, or combinations thereof in concrete structures.